When a high-speed signal propagates through a transmission medium such as a printed circuit board backplane, not all of the frequency components get attenuated equally. In general, high frequency components are attenuated more than low frequency components. The result is ISI (inter-symbol interference), which causes jitter in the ideal timing of a signal.
Equalization is a method to boost the high frequency components more than the low frequency components. Ideally the frequency response of the equalizer should be the inverse transfer function of the backplane or other transmission medium. The combination of the two transfer functions should ideally be flat for the frequencies of interest. The problem is that there may be many possible combinations of equalization solutions. It may therefore require a lot of time to determine the optimal setting. This is usually through trial and error.
An adaptive equalization block can take the burden off the user and determine the optimal setting. An adaptive equalizer includes an equalizer and an adaptation “engine” which chooses one of the possible equalization curves so that the combination of the two transfer functions is flat. Because of the benefits of using adaptive equalization, improvements to adaptive equalizer blocks are always being sought.